Differential scanning calorimetry (DSC) has been often used for determining the glass transition temperature of resin materials, but may fail to detect a signal originated from glass transition depending on the types of materials in some cases. Although, such cases have a drawback in that a relatively large amount of a material to be measured had to be prepared and formed into a sheet-shaped test piece or a fiber-shaped test piece, the loss tangent tan δ of those test pieces has been determined by dynamic viscoelasticity measurement in a tensile mode and the temperature at the maximum peak has been taken as the glass transition temperature of the measured resin material.
For a fine resin particulate material as used as a filler, by the way, the dynamic viscoelasticity measurement had to be performed inevitably because the aggregation of powders had a low thermal conductivity and thus the DSC failed to detect a signal originated from glass transition. However, being in the form of the fine particulate material has caused a problem with the dynamic viscoelasticity measurement either in a tensile mode or in a shear mode or in a three-point bending mode.
Accordingly, the dynamic viscoelasticity measurement of such fine resin particulate materials has required production of a sample having a shape capable of undergoing the dynamic viscoelasticity measurement. For example, it has been proposed that a composition in which 50 to 150 parts by mass of polymer resin particles are blended with 100 parts by mass of thermosetting epoxy resin is poured into a strip-shaped mold and cured to produce a strip-shaped test piece (Patent Literature 1). Furthermore, it has been proposed that a dispersion obtained by dispersing 100 parts by mass of acrylic polymer particles in 100 parts by mass of diisononyl phthalate was casted and heated to produce a sheet-shaped test piece (Patent Literature 2).